In older existing homes built in areas prone to earthquakes, brick chimneys may crack or be completely destroyed during an earthquake. If a brick chimney is significantly damaged during an earthquake it may cause bricks to fall to the ground possibly injuring persons or property nearby. To avoid this in certain cities and counties, earthquake standards for new chimney construction have been introduced. The Uniform Building Code sets minimum standards while cities may impose higher standards for new chimney construction. Furthermore certain cities have required that preexisting chimneys be brought up to code when any work is to be performed upon the masonry unit of a chimney or fireplace. Also, real estate sales contracts were written which required a seller to repair the fire, safety, and structural defects of older pre-existing chimneys upon the transfer of title to a home. Previously to meet building codes it required the removal of all or portions of the old chimney and then construction of a new chimney that would meet the building codes.
In older homes and geographic areas without earthquakes, chimneys may be non-reinforced. FIG. 1A represents a cutaway view of a non-reinforced chimney 112A resting upon a fireplace 110. The outer facade of the fireplace 110 and chimney 112, also referred to as the brick masonry unit 128, is made up of brick 160 and mortar 162. Within chimney 112A there is an airspace 103 and a chimney liner 104. Many older homes may not have the chimney liner 104 and rely on the brick masonry unit 128 to direct heat and smoke up through the chimney and out into the atmosphere.
Chimneys may be designed into a home in three broad categorical groupings. One group of chimneys may be designed and constructed such that the fireplace and chimney are external to a home and the back face of the chimney adjoins a homes wall for a significant portion of the chimney height. This first group will be referred to as "external wall chimney". A second group of chimneys may designed and constructed such that the fireplace and chimney are external to a home and the chimney is freestanding above the roof-line for a significant portion of the chimney height. This second group will be referred to as "external roof chimney". A third group of chimneys may be designed and constructed such that the fireplace is completely internal to the home and the chimney only rises above the roof for a short portion of the chimney. This third group of chimneys will be referred to as "internal chimneys". The construction codes for a given city will vary depending upon the above type of chimney that is designed and constructed in a home. For example, pre-existing internal chimneys require no horizontal reinforcement or anchorage because there is little danger that an internal chimney will fall on persons or property.
As earthquakes caused damage to chimneys in geographic areas prone to earthquakes, real estate sales contracts were written which required a seller to repair the fire, safety, and structural defects of older pre-existing chimneys upon the transfer of title to a home. Initially only a horizontal tie or anchorage at the roof-line or plating was installed. FIG. 1B represents early attempts to satisfy the horizontal reinforcement requirements for pre-existing external wall chimneys that were flush to a house wall. In FIG. 1B, chimney 112B has an external strap 120 attached to an external wall 125 by use of bolts 121. This is similar to a brace illustrated in U.S. Pat. No. Des. 285,411 invented by Nathaniel J. Mahoney having a filing date of Nov. 30, 1983. One disadvantage to the use of the external strap 120 is that chimney 112B may break or crack just above the external strap 120. Another disadvantage to the use of the external strap 120 is that the bolts 121 may break free from the wall 125 because of the pulling force exerted by the weight of the chimney is so large that the wall can not bear it. Generally the bolts 121 are inserted into holes in the wall 125 that have been drilled through cement. Another disadvantage to the use of the external strap 120 is that it does not satisfy the Uniform Building Code requirements for horizontal reinforcement and anchorage of preexisting chimneys. It is desirable that an external strap or anchor for a preexisting chimney be bolted to the internal frame of a house and meet current building code requirements.
As stronger earthquakes occurred, it became known that a horizontal anchorage such as illustrated by FIG. 1B was not enough to prevent parts of a chimney from falling in the case of the external wall or external roof chimney types. Vertical reinforcement was introduced into the pre-existing chimney. FIG. 1C illustrates an early attempt at providing the vertical reinforcement of a preexisting chimney in order to meet these initial codes. Chimney 112C rests upon a fireplace 110. A mortar cap 114 completes the top of the chimney 112C while a spark arrestor 116 is attached to either a chimney liner 104 or the mortar cap 114.
In order to reinforce the chimney and meet the initial codes, the mortar cap 114 was removed and a hole 106 was drilled into the mortar of the firebox at each corner of the chimney. A mortar cement 105 was placed in each hole 106 and steel rebar 100 of one-half inch or five-eights inch diameter extending the length of the chimney 112C was inserted into each hole 106. A mortar cement 102 was poured into the void between the brick chimney and the chimney liner 104 to further solidify the chimney. To reinforce the mortar cap, a bond beam 108 of two wraps of a No. 2 pencil steel rod was placed around the four steel rebars 100. While this technique met the earlier code for vertical reinforcement of pre-existing chimneys it did little to meet the horizontal reinforcement and anchorage required by newer codes. Also the use of cement as a filler added extra weight to a chimney such that foundations were unable to support it.
The 1991 Uniform Building Code for new home and new chimney construction in earthquake prone zones, such as seismic zone 4, require a chimney to be affixed to a house's frame in order that a chimney does not fall away from the house during an earthquake. FIG. 2A illustrates the use of a mason's anchor strap 220 that is attached to a wooden beam 221 by nut/bolt assemblies 222 and 223 that satisfies the 1991 Uniform Building Code seismic anchorage requirement for new chimney construction. The mason's anchor strap 220 is inserted into the chimney while it is being constructed. The wooden beam 221 is attached to the homes joists and the mason's anchor strap 220 is attached to the wooden beam 221 during the homes construction. Horizontal reinforcement in newly constructed chimneys is provided by horizontal reinforcing ties 208A-N at eighteen inch intervals using a minimum of one quarter inch diameter steel such as a number two pencil rod that horizontally ties the vertical steel rebars 100 together.
FIG. 2B illustrates a new mason's anchor strap 220 with the nut/bolt assemblies 222 and 223. The mason's anchor strap 220 has a flat tongue 234 with two holes 232 and 233 for bolting the strap to either wooden beam 221 or wooden beam 219. Having two holes 232 and 233 in the mason's anchor strap 220 reduces the strength of the strap and is disadvantageous. The flat steel tongue of the anchor strap 220 is twisted ninety degrees at 235 such that a hooked blade 236 is created. The hooked blade 236 is twisted around the steel rebar 100 such as illustrated in FIG. 2C and then the tongue 234 is bolted to the wooden beam 221 or 219. FIG. 2C illustrates how two mason's anchor straps 219 and 220 are wrapped around the steel rebar 100 in order to provide for horizontal reinforcement and anchorage of the chimney. As a mason constructs the chimney brick by brick and liner by liner, horizontal reinforcing ties 208A-N are added at eighteen inch intervals. A mason may also fill the area 205 between the masonry work 128 and the chimney liner 104 with mortar if it is a reasonably small area. A mason continues in this manner in order to construct a new chimney having horizontal and vertical reinforcement.
Use of the mason's anchor strap 220 on preexisting chimneys physically requires that a chimney be at least broken down to the roof line. Installation of the horizontal reinforcing ties 208A-N at eighteen inch intervals requires that a majority of a pre-existing chimney be dismantled. Other codes in some cities require a pre-existing chimney to be completely broken down to the fireplace and then completely rebuilt in order to insert the mason's strap and horizontal reinforcing ties. After installing the mason's anchor strap 220 in a chimney, the mason must reconstruct the remaining portion of the chimney using new mortar. Dismantling a preexisting chimney and reconstructing a new chimney requires an expensive investment in labor and new materials. It is desirable that a preexisting chimney be retrofitted to meet horizontal reinforcement requirements without partially or completely removing the existing brick chimney thereby reducing the investment in labor and materials. It is desirable that a preexisting brick chimney be anchored to the house without partially or completely removing the existing brick chimney.